Holding fixture for coating optical elements



Nov. 9, 1948. w, LANGE 2,453,141

HOLDING FIXTURE Fon coA'rI'uG oP'JJIcAL ELEMENTS I .Filed Aug. 7. 1945 2 Sheets-Sheet 1 ,y

Nov. 9, 1948,. w. LANGE HOLDING FIXTURE FOR COATING OPTICAL ELEMENTS Filed Aug. 7, 1945 @My/1f MMJ I 2 Sheets-Sheet 2` WERNER LANGE Patented Nov. 9, 1.948

UNITED STATES PATENT OFFICE HOLDING FIXTURE Fon coA'rING orrrosr. ELEMENTS 4 Claims.

amended April 80. 1928: 870 0. G. '157) The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

My invention relates to devices for supporting glass or other optical elements upon whose surfaces a transparent or other coating is to be applied and it has special reference to element holding devices intended for use in the thermal evaporation method of applying such coatings.

One object of my invention is to provide a device for holding prisms and lenses in a manner which will not interfere with the area of glass to be coated.

vAnother object is to provide a device which is capable of simultaneously holding a quantity of prisms and lenses having various sizes and shapes in such a way that the surface of each element to be coated is equidistant from the vaporizing coating material, thereby making possible uniformly thick coats on each.

A further object is to provide such a holder which can be readily adjusted for quick, accurate and easy assemblage oi differently sized and shaped prisms and lenses.

An additional object is to provide a holding fixture which can be handled easily and conveniently when carrying its full capacity of prisms, lenses or other elements assembled thereon.

In practicing my invention I attain the foregoing and other objects by providing an .optical element holding fixture of unique adjustable construction and superior practical performance. One preferred form of such a fixture is shown by the accompanying drawings wherein:

Fig. 1 illustrates my novel holder for prisms and lenses installed in a vacuum chamber equipped for thermal evaporation of metallic salts and represented in longitudinal section with part of the electric heating unit cut away;

Fig. 2 is a top plan view of the uniquely adjustable optical element holding ilxture of Fig. 1;

Fig. 3 is a section on line 3--3 through two of the ilanged holding rails of Fig. 2 showing an optical element supported therebetween;

Fig. 4 is an enlarged showing of a bolt and clamp nut used to ilx the holders prism and lens supporting rails in desired position; and

Fig. 5 is a section on line 5-5 of Fig. 2 showing the manner of clamping a rail to the flxture's latticework.

Problem which my holding fixture solves The optical manufacturing art has in recent lyears experienced a considerable increase in use of coatings applied to the surface of glass with the principal object of obviating or enhancing reflection of the well-known "Fresnel'? rays. One of the most satisfactory methods of applying such coatings to optical glass has been the evaporative deposition of metallic fiuorides in a vacuum under high temperatures.

As the fluoride salt is vaporized in an open crucible,'its vapors radiate in all directions above the surface of the container. It has long been known that the thickness of coating which built up on a glass surface by this process was largely dependent upon and inversely proportional to the distance separating the glass from the solid fluoride salt whose vapors were being disseminated.

It has become obvious, therefore, that to simultaneously and uniformly coat a number of prisms or lenses during a single evaporation of the fluoride substance. it would be desirable to position the glass blanks so that, in effect, they form al spherical arch whose center of curvature coincides with the source of 'fluoride vaporization. The prior art has accordingly developed holding fixtures having such a dome shape. One such device is tted with recesses individually designed to support a particular size and shape of prism or lens. While such a holder is serviceable, its shortcomings lie in its lack of adiustability to hold the various forms of optical glass. Thus it has been necessary to have a large number of such racks custom-built for each type or size of lens or prisms.l This uneconomical practice has. in turn, impaired the eiilciency of the coating process. For example, where it is desired to coat a batch of glass whose representative types include several different dimensions and designs, there is required the separate use of a ixture and a separate coating operation for each of the several variations.

A modification of this old type holding device consists of a similar dome-shaped fixture having recesses designed to support variously sized and shaped prisms and lenses. Thisalso is not satisfactory, it being inefficient top lack of adjustability. If a batch of glass to be coated includes a surplus of one particular size and a deilciency of another, no use can be made of the glass'blank retaining recesses left vacant by the latter condition. Hence, here again a separate coating operation must be performed for each variation, which procedure is -wasteful of time and of the uoride salt used.

From the foregoing, it will be apparent that a holding iixture which essentially possesses the 36 cut into the rails sides.

required spherical or dome shape. and which can be readily adjusted to accommodate practically all shapes and sizes of optical glass. will fulfill a useful and practical function.

That my herein disclosed invention possesses these desirable universal features will become evident as the description hereof proceeds.

Construction of improved adjustable holding fixture From the drawings it will be seen that my improved holding flxture consists of a portable truncated pyramidal framework whose frame members are so spaced that the iixture's overall contour essentially simulates a. spherical segment. This framework is preferably made of a light metal (such as aluminum) which is capable of withstanding high heat. One size found to be convenient for handling is approximately 18 inches in diameter by 3% inches high. Essentially, the fixture parts include a circular base portion i0, eight "ramps" Ii to i8 equidistantly attached to this base, and two strips l9-20 each serving to join and support a group of four of those ramps as shown. Thus constructed, the iatticed fixtures subdivisions may for convenient reference be labeled lateral sections A to H and the top J (see Fig. 2).

Additional serving to brace ramps li to i@ as well as to support an adjustable prism or lens shelf thereon are eight small ramps 2l to 26 distributed equally among each of the four lateral sections A, C, E, G. Also located in each of those sections are pairs of strips 3i to 3d, attached as shown in Fig. 2, and each bearing a shelf for holding an optical glass piece. Similar shelving strips fiS--d are respectively attached to the sides of the two top members i9 and 20.

Each ramp il to i6 and 2l to 28, as well as the top members l9-20, have over almost their entire lengths vertical slots 38 extending therethrough. In these slots are fastened cross rails typified by the straight and curved designs shown aty 39 and 60, respectively.

The fastening means used to position those crossl rails may suitably comprise a, bolt il and clamp nut d2 of the type shown'in Figs. 4-5. The slender vertical column of nut 42 is capable of slidably fitting into the slots 38 in framework parts il to 28; the nuts flat base portion acting to wedge it tightly against the ramps and other framework parts under side of those parts. To fasten the rail at a desired point between parallel ramps or tie strips il to 28 in any of the iixtures sections, bolt di is passed through a hole in the flange at each end of rails 39-40 to thus threadably engage the clamp nut 82 in the aforementioned slots 38 therebeneath as shown in Fig. 5.

Qperation of my improved holding fixture As will be apparent from the description and illustrations of my fixtures construction, operation of the improved holding device is exceedingly simple. For example, a pair of parallel straight rails 39 may be loosely fastened across a pair of parallel ramps il to I8 and 2| to 26 or top strips I9-20 in the manner previously outlined. Next, a row of lenses 49 or prisms 50, all of which are of equal width across the surfaces to be coated,

c is placed between the rails 39 so that these glass surfaces rest face downward upon narrow shelves The width of these shelves 36 alters the amount of glass surface area. which can be coated; by making them extremely narrow, on the order of 31g inch wide as shown in Fig. 3, a maximum amount of glass surface is exy posed to the vapors of, the coating substance which deposit thereon.

The parallel rails are then brought as closely together as the intervening lenses or prisms permit, and finally the bolt lil-to-clamp nut 42 connection of Fig. is made fast. By this means the rails aremade to exert lateral clamping pressure i are not enough of these pieces to warrant using the space which would be required between two parallel straight rails, a curved rail 40 may be conveniently utilized as shown in Fig. 2.

Such flexibility in mounting an assortment of sizes and shapes of glass pieces on my iixtures latticework so that they may ice-coated in a single operation of the coating mechanism makes possible the superior eiciency earlier described. Gone is the need to' use a separate xture for each glass form variation and likewiseleiiminated is the need to separately coat each group of individual optical glass types.

Typical process utilizing improved holding fixture The operation and usefulness of my improved holding device will become even more apparent by illustrative reference to one process and apparatus in which it has been extensively used. This process is concerned with reducing reflections from the surface of optical glass by baking thereon, in a substantial vacuum, a quarter wave length coating of vaporized magnesium fluoride.

Used in this process is a coating apparatus which includes my unique holding fixture as shown in Fig. 1. constituting the vacuum'chamber is a bell jar 60 and a base plate 6l upon which the jar rests, forming an airtight seal. Suitable vacuum pumps (not shown) communicate with exhaust opening 62 in the base plate and are effective to evacuate the chamber to a pressure of 10-4 millimeters of mercury or better.

Supported on a tripod 63 is a crucible 64 made I of ceramic or other material capable of withstanding great heat. This crucible is filled with chemically pure salts of magnesium fluoride. A 0.035 inch tungsten-chrome filament constituting part of an electrical circuit is arranged so that approximately four small turns of the wire are lsoscated over the crucibles mouth as indicated at Sections A-B--C of the Fig. 2 fixture, stripped of supporting rails and optics, c'an be seen in the Fig. l view which depicts the device supported by a large ringstand 66. A number of optical glass pieces 50 may also be seen protruding from their supports in section J of Fig. 2. Covering the lixture and these glass pieces' is an electrically heated metal shield 61 which also rests on, ringstand 66.

`To eiect a coating of the optical glass lblanks 60, the chamber is first evacuated to a pressure of 10-4 millimeters. The heated shield 61 is 'raised to a minimum temperature of 200 F. (and preferably to 500 F. for superior performance. This heat permeates the glass blanks 50- `and raises their temperature to a point where the inagnesium fluoride about to be condensed .thelbn WERNER LANGE. 5

REFERENCES CITEn The following references are of record 1n the me of this patent: 1

Number UNITED STATES PATENTS Name Date Rosenfeld Oct. 11, 1875 Patton Oct. 13, 1903 Vokes Jan. 27, 1942 Lee June 16, 1942 Hewlett Dec. 21, 1943 Sukumlyn Feb. 15, 1944 Wampler Aug. 22, 1944 Lyon Apr. 16, 1946 

